In general, a hydraulic excavator which is a typical example of a construction machine is composed of an automotive lower traveling structure, an upper revolving structure rotatably mounted on the lower traveling structure, and a working mechanism capable of moving upward/downward on the front side of the upper revolving structure.
The upper revolving structure is composed of a revolving frame forming a support structural member, an engine mounted on the rear side of the revolving frame, and a cab provided on the left front side of the revolving frame so as to follow the left side of the working mechanism. In the cab, an operator's seat on which an operator is seated and the like are provided.
On the revolving frame, a fuel tank located on the right side of the working mechanism and storing fuel to be supplied to the engine is provided. On the front side of the fuel tank, a toolbox accommodating articles such as a tool, a grease gun, various consumables and the like is provided.
On the other hand, a diesel engine is used for an engine of a hydraulic excavator. This diesel engine is said to emit a large quantity of nitrogen oxides (hereinafter referred to as NOx) and the like. Thus, as a post-treatment device of an exhaust gas of a diesel engine, a NOx purifying device for purifying NOx is known. This NOx purifying device is composed of a urea selective reduction catalyst provided in an exhaust pipe of an engine, for example, for removing nitrogen oxides in the exhaust gas, a urea water tank storing a urea aqueous solution (urea water) as a reducing agent, a urea water injection valve arranged on the upstream side of the urea selective reduction catalyst in a flow direction of the exhaust gas and injecting urea water to the exhaust gas, and a connection pipeline connecting the urea water tank and the urea water injection valve.
Here, when a urea water tank is to be provided on a hydraulic excavator, a tank volume is preferably set larger in order to reduce the number of times of solution supply. However, since a large number of devices are mounted on the hydraulic excavator, it is difficult to ensure a new space on which a urea water tank is to be installed. Thus, a hydraulic excavator according to a conventional art is configured such that a urea water tank is accommodated in a toolbox for accommodating tools and the like (Patent Document 1).